Noninvasive compound ultrasound elastography for vulnerable plaque detection: in vivo validation

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Purpose: Carotid stenosis with plaque rupture is one of the main underlying causes of stroke. Key issue in the risk assessment is identification of the plaque prone to rupture. We developed a noninvasive method to estimate deformation (strain) in a carotid plaque. In this in vivo validation study the relation between measured strain and histological plaque vulnerability was assessed. Methods: Raw ultrasound radio-frequency (RF) data were recorded in vivo of 18 severely stenotic (>70%) carotid arteries of symptomatic patients before carotid endarterectomy (CEA). Radial strains in each vessel wall were estimated with compound elastography in a transversal plane at the site of highest stenosis using dedicated signal-processing algorithms that combined RF data from three different acquisition angles. To record at the multiple angles without repositioning the used L5-13 linear array transducer, a Medison Accuvix V10 ultrasound system with a custom made imaging sequence was used. For each plaque the percentage of plaque area with strain values above 1.5% was determined. After CEA, the segments of highest stenosis were cut and histologically stained. The sensitivity and positive predictive value (PPV) of the strain area parameter were determined for the detection of a thin fibrous cap, a large lipid pool, a high concentration of superficial macrophages, and a lack of smooth muscle cells (SMCs). Results: Table 1 shows the results for the 18 plaques. As shown the estimated strains are clearly related to plaque vulnerability features. The highest sensitivity and PPV were observed for thin fibrous caps and superficial macrophages: 80% and 80%, and 100% and 100%, respectively. View this table: Table 1. Sensitivity and positive predictive value (PPV) for the detection of 5 histological features of plaque vulnerability using the strain area parameter Conclusions: Within an in vivo setting, we confirmed that compound elastography provides a validated noninvasive assessment of plaque vulnerability features.